Browsing by Author "Julia, Jordi"

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    Upper-mantle low-velocity zone structure beneath the Kaapvaal craton from S-wave receiver functions
    (Oxford University Press, 2009) Hansen, Samantha E.; Nyblade, Andrew A.; Julia, Jordi; Dirks, Paul H. G. M.; Durrheim, Raymond J.; Pennsylvania Commonwealth System of Higher Education (PCSHE); Pennsylvania State University; Pennsylvania State University - University Park; University of Witwatersrand; University of Alabama Tuscaloosa
    P>The southern African Plateau is marked by anomalously high elevations, reaching 1-2 km above sea level, and there is much debate as to whether this topography is compensated by a lower mantle source or by elevated temperatures in the upper mantle. In this study, we use S-wave receiver functions (SRFs) to estimate the lithospheric thickness and sublithospheric mantle velocity structure beneath the Kaapvaal craton, which forms the core of the Plateau. To fit the SRF data, a low-velocity zone (LVZ) is required below a similar to 160-km-thick lithospheric lid, but the LVZ is no thicker than similar to 90 km. Although the lid thickness obtained is thinner than that reported in previous SRF studies, neither the lid thickness nor the shear velocity decrease (similar to 4.5%) associated with the LVZ is anomalous compared to other cratonic environments. Therefore, we conclude that elevated temperatures in the sublithospheric upper mantle contribute little support to the high elevations in this region of southern Africa.
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    Using S wave receiver functions to estimate crustal structure beneath ice sheets: An application to the Transantarctic Mountains and East Antarctic craton
    (American Geophysical Union, 2009) Hansen, Samantha E.; Julia, Jordi; Nyblade, Andrew A.; Pyle, Moira L.; Wiens, Douglas A.; Anandakrishnan, Sridhar; Pennsylvania Commonwealth System of Higher Education (PCSHE); Pennsylvania State University; Pennsylvania State University - University Park; Washington University (WUSTL); University of Alabama Tuscaloosa
    For seismic stations deployed on ice sheets, determining crustal structure using P wave receiver functions can be difficult since ice reverberations may mask P-to-S (Ps) conversions from the crust-mantle boundary (Moho). In this study, we assess the usefulness of S wave receiver functions (SRFs), which are not affected by ice multiples, for investigating crustal structure beneath ice sheets by analyzing broadband seismic data recorded across the Transantarctic Mountains (TAMs) and the East Antarctic (EA) craton. Clear S-to-P (Sp) conversions from the Moho are obtained using standard SRF processing methods and are easier to interpret than the corresponding Ps conversion on PRFs. When the Sp-S times are modeled together with 16-20 s Rayleigh wave group velocities, we obtain Moho depth estimates of similar to 40-45 km for the EA craton, consistent with average Precambrian crustal thickness found globally but similar to 9 km thicker than previously reported estimates. A somewhat thinner crust (similar to 35-40 km) is obtained beneath the TAMs, suggesting that crustal buoyancy is at most a minor contributor to the uplift of the mountain range in this region.